1. Field of the Invention
The present invention relates generally to antennas for transmitting and receiving electromagnetic radiation, and more particularly, to a monocone antenna combined with one or more other antennas and all are fed from a single RF feed point. This antenna effects highly efficient transmission and reception of electromagnetic radiation over a very wide range of frequencies.
2. Description of the Prior Art
Antennas for transmitting and receiving radiation in the form of a monocone, also known as a conical monocone or a conical monopole or a unipole is known.
Also known is a discone antenna which is a combination of a disk and a cone antenna, as differentiated from a monocone. A conical skirt monopole is also very similar to a discone.
The Antenna Engineering Handbook (1984), Section 26-4, by Johnson and Jasik describe a conical monocone and an inverted cone as broadband monopole antennas, and in Section 27-4 describe discone antennas. Rudge, et. al., in the Handbook of Antenna Design (1986) on pages 1378-9 describes a conical monopole and a double-cone monopole, and on pages 1427 and 1432 describe discone antennas. These two handbooks also describe thin monopole xe2x80x9cwhipxe2x80x9d antennas, and inverted-L antennas.
Balanis in Antenna Theory and Analysis (1982) on page 330 describes a Unipole, which is the same as a monocone, and on pages 330-332 describes Triangular Sheet, Bow-Tie, and Wire Simulation antennas, and on page 346 describes Discone and Conical Skirt Monopoles. C. M. Knop and R. Frazer also disclose and study a monocone in xe2x80x9cA Study of Small-Height HF Jarriming Antennas for Vehicular Usexe2x80x9d, pages 267-274 of Microwave and Optical Technology Letters, Vol. 13, No. 5, December 1996.
U.S. Pat. No. 6,198,454 issued to Sharp teaches direction finding antennas using monocones and bicones. Claims 1-7 of Sharp only claim a single antenna (monocone or bicone), there is no second or additional radiators in claims 1-7. In claims 1-12 Sharp never claims a full 360 degree monocone or bicone, only sectors of a cone, or flat antennas, only in claim 13 does Sharp claim a full 360 structure but gives no specifics regarding the structure, only describing it by it""s performance.
In claims 8 thru 13 and FIGS. 6 and 7 Sharp U.S. Pat. No. 6,198,454 describes a direction finding array antenna. Sharp describes that different signals are received at a receiver from different antennas of the Sharp array, so that these signals may be compared. This would not be possible if the signals from all the antennas in the array were combined at one RF feed port into one feed transmission line.
See Sharp col. 1 lines 36-40 which states xe2x80x9cDirection finding antenna arrays determine direction by comparing the phase or strength of signals received at different antennas.xe2x80x9d
Also see column 8 lines 20-26 which states xe2x80x9cdirection finding arrays generally operate by comparing the phase of the signals received by antennas arranged in an array. Information about direction may also be derived from the amplitude of the signals received from antennas facing in different directions in an arrayxe2x80x9d.
Also see column 2 lines 52-53 xe2x80x9cmeasuring the phase of the signals from the plurality of direction finding antennas.xe2x80x9d
It is clear from these statements that Sharp separately measures the phase and/or amplitude of more than one antenna in his array so they can be compared. This is not possible with only one feed transmission feed line used simultaneously for the entire array antenna. Multiple feed transmission lines are used, each to a different part of the array. These may be all connected to a switch, but the RF signals are not combined simultaneously when receiver needs to make a comparison.
Therefore, in Sharp FIGS. 6 and 7 and claims 8 thru 13, multiple antennas are used with multiple feed transmission lines to different parts of the antenna. The lines drawn in FIGS. 6 and 7 connecting the different antennas simply represent the feed transmission lines as they are each connected to each antenna. Those lines do not represent that the feed transmission lines or the antennas are all electrically connected to each other. Each portion or each antenna of the Sharp array has a separate RF port with separate feed transmission line from each antenna to the receiver.
Unlike Sharp U.S. Pat. No. 6,198,454 our antenna has one single feed transmission line from the receiver/transmitter to the entire antenna. Our single feed transmission line from the receiver/transmitter feeds our monocone, the signals from our entire structure, including all antennas, is received simultaneously at this single RF feed port at all times. Our additional radiators are always connected to the first radiator (our first radiator being the monocone).
A last consideration regarding Sharp U.S. Pat. No. 6,198,454: our provisional patent Application No. 60/156,948 filed on Sep. 30, 1999 describes our antenna, the date of this report is Jul. 5, 1999 which pre-dates the Sharp application date of Jul. 16, 1999.
U.S. Pat. No. 5,990,845 issued earlier to Sharp recites, in claims 1 through 16 and claims 19 through 23, a single partial cone fan antenna, there is no second antenna or plurality of antennas in these claims. Claim 17 and 18 of Sharp U.S. Pat. No. 5,990,845 does claim a second partial cone which is a reflection of the first partial cone, to form a single bicone which is a well known type of antenna consisting of two monocones arranged with apexes close together. These two monocones comprising the bicone are not electrically connected to each other, and this antenna is not fed from the apex of a single monocone since it is fed using the apex of both monocones, and there is no additional antenna connected to this bicone. Moreover, all the claims of Sharp U.S. Pat. No. 5,990,845 explicitly claim a partial cone shape, ie cone sweep angle less than 360 degrees. None of the claims claim a full 360 degree monocone or bicone.
U.S. Pat. No. 5,038,152 issued to Wong describes a dielectric rod antenna. In the field of the invention Wong states that: xe2x80x9cMore specifically, this invention relates to dielectric rod antennasxe2x80x9d. Claim 1 of Wong specifically refers to a tapered dielectric rod extending through said aperturexe2x80x9d. The primary radiator in Wong is a dielectric rod and the dielectric rod is the first antenna fed from Wong""s feed aperture, the monocone is not the, primary radiator. In our invention the monocone is the primary radiator and is the first antenna fed. In Wong the other radiators (Wong""s parasitic elements 32, 34, 36, and 64) are not electrically connected to the monocone, they are connected to a mast which is connected to the dielectric rod, the mast is not connected to the monocone (claims 1,2,3,4). In Wong the monocone is not inverted, in our invention the cone is inverted with the apex fed at the ground plane. Wong does not use a ground plane. The feed structure and feed operation in Wong is completely different. Wong""s invention is fed from a circular waveguide (claim 1), which is well known to be a hollow waveguide type of transmission line with no center conductor. Energy is coupled from the circular waveguide to Wong""s dielectric rod. Wong""s cone is connected to rim or to the outside of the circular waveguide. This is not how a monopole or monocone is typically fed. Our monocone is fed from the center conductor of a coaxial type of transmission line, in the manner in which a monopole antenna is typically fed. Our monocone is not connected to the rim or outside of the coaxial feed line. In Wong, the monocone is located below the feed aperture point, with the other radiators (the tapered dielectric rod and the parasitic elements) located above the feed aperture point. In our antenna the monocone and all other antennas are located above the feed point. The monocone in Wong is therefore more similar to the cone used in a discone antenna than to the monocone in our invention. In Wong the monocone functions to redirect the electrical energy, it is electrically more similar to a ground plane or reflector. In our invention the monocone functions as the primary radiator, not as a redirector or conical ground plane.
U.S. Pat. No. 3,534,378 issued to Smith teaches a wide band antenna for producing substantially omnidirectional horizontal coverage and an upwardly tilted torodial vertical coverage. The Smith antenna has, in combination, a cylindrical conductive means of length corresponding substantially to the half-wavelength of a frequency at the low end of the specified wide band with ground plane means comprising a plurality of substantially co-planar conductors of different lengths providing paths of substantially the half-wavelengths of frequencies at both the low and high end of the said wide band and slightly spaced from one end of the cylindrical conductive means to define a slot there between. Smith also describes current suppressing means a distance from one end corresponding substantially to a half-wavelength of a frequency at high end of the band in order to suppress the propagation of such high frequency currents and also describes a means for simultaneously feeding currents of different frequencies lying within the band between the ground plane and one end of the cylindrical conductive means across the slot. Smith teaches that the ground plane conductors comprise spaced radially conductors.
U.S. Pat. No. 3,618,107 issued to Spanos teaches a broadband discone antenna arrangement achieved by combining an auxiliary conical element coaxially mounted with respect to the axis of the first conical element (main cone) and the center of the disc element, and situated there between. Said second conical element is fed by the inner surface of the outer conductor of the coaxial transmission feed line.
Neither Sharp nor Wong nor Smith nor Spanos nor others known teach that a monocone on any suitable ground plane can be electrically connected to one or more additional antennas, all fed simultaneously from a single feed point, using a single feed transmission line, to achieve larger bandwidth and greater efficiency at equivalent or smaller size than would said antennas when employed as individuals. Nor is it anywhere taught to impedance match, not suppress, high frequency currents by electrically connecting the monocone with additional antennas described herein close to the common RF feed point. Further the inventive antenna described herein requires no choke, as taught by Smith and others.
Thus, while the foregoing body of prior art indicates it to be known to use monocone antennas, the prior art does not teach or suggest a monocone antenna combined with one or more additional antennas in such a way as described herein thus to be used to achieve broader band transmission or reception than when each antenna is used individually. This also results in a more compact and cost effective device than the monocone and the other antennas constructed and used individually.
The disadvantages of the foregoing are overcome by the unique antenna design of the present invention as will be made apparent from the following description thereof. Other advantages of the present invention over the prior art also will be rendered evident.
An ultra broadband antenna is provided by combining a monocone antenna with one or more additional antennas described herein, and all are connected together electrically near a single feed point for the entry and exit of radio frequency (RF) electromagnetic signals to and from the antenna. The said feed point is at the apex of the monocone. The inventive combination antenna has a greater frequency bandwidth than the monocone, and greater bandwidth than any of the other antennas when employed singly.
It is known that an antenna may be either a radiator or receiver of electromagnetic signals, also generally referred to as xe2x80x9cradio frequencyxe2x80x9d (RF) signals. The feed point of the antenna is the locus of where the electromagnetic signals are fed to and received from said antenna, said electromagnetic signals being those radiated from or received by the antenna.
Further it is known that a monocone antenna may be constructed of one or more conductors defining a conical surface, and that the conductor or conductors forming the monocone may be solid; partially solid; a surface; a wire grid; or wires connected near the apex of the monocone; or an array of conductors disposed conically about a common feed point; and each of the wires or conductors in the array need not be of the same length in defining said cone. A monocone with a full flare angle of less than approximately 5 degrees is essentially the same as a monopole.
The ultra-broadband antenna of the invention is formed by combining a first radiator, which is a monocone, with one or more additional antennas referred to herein as additional radiators or as the second and subsequent additional radiators. The additional radiators may be the same type as each other or of different type from each other. The additional radiators are typically selected from the group consisting of monopole, whip antenna, loaded monopole, top-loaded monopole, triangular sheet antenna, fan monopole, inverted L antenna, and loop antenna.
The additional radiators are affixed to the first radiator and are electrically connected close to the feed point of the first radiator, this would include being connected to the first radiator at an electrically small distance from the feed point to the first radiator. xe2x80x9cElectrically closexe2x80x9d and xe2x80x9celectrically small distancexe2x80x9d are defined here as much less than one wavelength at the lowest frequency of operation, for example 0.15 wavelengths would be electrically close. This electrical connection is a direct physical connection, not by a length of transmission line. An electrical connection at radio frequencies could include a path for conduction current or a path for significant xe2x80x9cdisplacementxe2x80x9d current, ie capacitive or inductive coupling.
The additional radiators are typically 50% or more longer than the monocone so that the monocone provides the impedance match to 50 ohms at the higher frequencies and the additional radiators provide operation at some lower frequencies.
The above brief description sets forth rather broadly the more important features of the present invention in order that the detailed description of embodiments thereof that follows may be better understood, and in order that the present contributions to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject matter of the claims appended hereto.
In this respect, before explaining the invention in detail, it is to be understood that the invention is not limited in its application to the details of the construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood, that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for designing other structures, methods, and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.
It is therefore an object of the present invention to provide an ultra-broadband antenna by combining a monocone with several other antennas, either singularly or in combination therewith.
It is an object of the present invention to provide an ultra-broadband antenna including means for utilization with any ground plane or ground structure suitable for a monocone and the additional radiators. It is an object of the present invention to provide an ultra-broadband antenna which can be conveniently mounted on vehicles: including automobiles, trucks, ships, aircraft, spacecraft, missiles, satellites or such acting as a ground plane for the antenna.
These together with still other objects of the invention, along with the various features of novelty which characterize the invention, are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and the specific objects attained by its uses, reference should be made to the accompanying drawings and descriptive matter in which there are illustrated preferred embodiments of the invention.